1. Field of the Invention
The present invention relates to image capturing apparatuses and control methods thereof, and particularly relates to image capturing apparatuses, used for shooting still images, that have functions for displaying a live view image that is a moving picture or functions for detecting subjects using moving pictures, as well as to control methods for such apparatuses.
2. Description of the Related Art
Thus far, image capturing apparatuses for shooting still images have had functions for displaying a subject image obtained by an image sensor as a live view image. For example, a digital camera disclosed in Japanese Patent Laid-Open No. 2001-078072 is provided with a low-pixel count image sensor for capturing a live view image and a moving picture processing circuit in addition to a high-pixel count image sensor for capturing still images, and an output from the image sensor for capturing the live view image is developed by the moving picture processing circuit into an image that is then displayed in a display device.
Meanwhile, in a digital camera device disclosed in Japanese Patent Laid-Open No. 2001-128036, an output from an image sensor used to capture still images is thinned when displaying a live view image, after which live view image data is generated by a live view image processor and displayed in a display device. During continuous shooting, the display of the live view image is prohibited, the live view image is displayed intermittently, or the like in accordance with a mode that has been set.
Furthermore, in a digital camera disclosed in Japanese Patent Laid-Open No. 2002-158901, during continuous shooting, an output from an image sensor used for capturing still images is stored in a buffer memory, resized to a display size, subjected to live view image processing, and displayed.
However, with the conventional technique disclosed in the aforementioned Japanese Patent Laid-Open No. 2001-078072, it is necessary to provide a mechanism that divides an optical path for the image sensor used for capturing still images and the image sensor used for the live view image. In the case where this mechanism is, for example, a movable mirror in a single-lens reflex camera, there is a disadvantage in that the live view image cannot be displayed when the mirror is up during continuous shooting.
Meanwhile, with the conventional technique disclosed in Japanese Patent Laid-Open No. 2001-128036, prohibiting the live view image display during continuous shooting makes it difficult to follow a subject such as when shooting a moving object, whereas it is difficult to view the image being displayed in the case where the live view image is displayed intermittently.
Furthermore, with the conventional technique disclosed in the aforementioned Japanese Patent Laid-Open No. 2002-158901, the output from the image sensor for still images, which is accumulated in a buffer memory when displaying the live view image during continuous shooting, is resized and then processed for live view image display, which results in increased display time lag. There is a further disadvantage in that prioritizing the live view image display processing when the still image development time is not sufficiently low relative to the frame rate will result in the still image development being late.
In addition to the live view image display, a similar problem occurs in a function for detecting a subject from a live view image obtained by an image sensor. A function for detecting the face of a person from an image signal, a function for following a subject by extracting regions of high correlation with regions specified as a subject in later frames, and so on can be given as examples of subject detection functions.
Even if a single-lens reflex camera is provided with an image sensor for capturing still images and an image sensor for detecting a subject, subjects cannot be detected in the case where continuous shooting is carried out with the mirror up. Furthermore, because a lengthy development process is required for image signals obtained by capturing still images, detecting a subject from an image signal obtained by capturing a still image will result in increased time lag until the subject detection result is obtained. It is therefore highly possible that the position of the subject will already have shifted by the time the subject detection result is obtained.